The present invention relates to an electrical motor with axially displaceable rotor there being a stator winding and the rotor is movable axially in relation to the stator; the axial shift of the rotor is carried out against a brake spring; the spring basically provides for a shift of the rotor between a running disposition and a stopped disposition; the rotor is mounted on a shaft to rotate therewith which shaft is journaled in housing plates of the motor.
A motor of the type to which the invention pertains is shown in e.g. German patent No. 1,015,117. Two different kinds of axially displaceable motors are known. In one kind rotor and shaft are a unit in that they are secured to each other. Shaft and rotor, thus, shift axially as a unit between a brake position and a running position. This approach is disadvantaged by the fact that the bearing for the shaft, particularly roller bearings, are to be designed to permit this axial displacement and it is therefore inherent that certain friciton losses do occur. High friction losses arise particularly during start-up of the motor particularly as the motor shaft output pinion operating the first gear in a transmission output stage, is also being shifted as an inherent result of the shift of the shaft. This additional frictional component can lead to immediate stalling of the motor upon turn-on. Moroever, owing to these additional axial shifts and forces in the gear, that first gear stage cannot be provided with a helical gearing, but regular axial gear arrangement leads to unduly high noise development.
The other kind of motors with axially shiftable rotor provides for a rotor assembly which is axially movable on the shaft. In order to transmit torque a special gear with involute helical gears or special ball gearings are needed. Again, it must be said that these known constructions are disadvantaged by high friction losses and actually the gearing of this complicated configurations may be deflected. The ball gear moreover is a very expensive item and also are prone to deflect. The axial shift during start-up is also here carried out against high friction forces corresponding to the high start-up moment of the motor.